Journal Article

The planetary system host HR 8799: on its <i>λ</i> Bootis nature

A. Moya, P. J. Amado, D. Barrado, A. García Hernández, M. Aberasturi, B. Montesinos and F. Aceituno

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 406, issue 1, pages 566-575
Published in print July 2010 | ISSN: 0035-8711
Published online July 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.16699.x
The planetary system host HR 8799: on its λ Bootis nature

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HR 8799 is a λ Bootis, γ Doradus star hosting a planetary system and a debris disc with two rings. This makes this system a very interesting target for asteroseismic studies. This work is devoted to the determination of the internal metallicity of this star, linked with its λ Bootis nature (i.e. solar surface abundances of light elements and subsolar surface abundances of heavy elements), taking advantage of its γ Doradus pulsations. This is the most accurate way of obtaining this information, and this is the first time that such a study is performed for a planetary-system-host star. We have used the equilibrium code cesam and the non-adiabatic pulsational code graco. We have applied the frequency ratio method (FRM) and the time-dependent convection theory to estimate the mode identification, the Brunt–Vaïsälä frequency integral and the mode instability, making the selection of the models possible. When the non-seismological constraints (i.e. HR 8799’s position in the Hertzsprung–Russell diagram) are used, the solar abundance models are discarded. This result contradicts one of the main hypotheses for explaining the λ Bootis nature, namely the accretion/diffusion of gas by a star with solar abundance. Therefore, according to this result, a revision of this hypothesis is needed. The inclusion of accurate internal chemical mixing processes seems to be necessary to explain the peculiar abundances observed in the surface of stars with internal subsolar metallicities. The use of the asteroseismological constraints, like those provided by the FRM or the instability analysis, provides a very accurate determination of the physical characteristics of HR 8799. However, the dependence of the results on the inclination angle i still remains. The determination of this angle, more accurate multicolour photometric observations and high-resolution spectroscopy can definitively fix the mass and metallicity of this star.

Keywords: stars: abundances; stars: chemically peculiar; stars: fundamental parameters; stars: individual: HR8799; planetary systems; stars: variables: general

Journal Article.  7243 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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